We propose a new theory of the demographic transition based on the evidence
that body development during childhood is an important factor for life expectancy.
The key and novel mechanism of the model is that parents face a tradeoff between
the quantity of children and the childhood development spending they afford on
each of them. It is in this sense that we refer to Wordsworth’s aphorism that “The
(Father of) Child is the Father of Man.” This tradeoff makes life expectancy and
fertility move in opposite direction. Along these lines, we propose a continuous
time model where fertility, childhood development, longevity, education and income
growth result all from individual decisions. The dynamics display the key
features of the demographic transition, including the hump in population growth,
and replicate the observed rise in educational attainments and life expectancy.
Consistent with the empirical evidence, a distinctive implication of our theory is
that childhood development leads the rise in education.